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Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - USD ($)
$ in Thousands
Sep. 30, 2023
Dec. 31, 2022
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 17,041 $ 24,999
Regulatory assets, long-term 89,491 94,655
Regulatory liabilities, current 32,285 17,300
Regulatory liabilities, long -term 275,809 244,497
Deferred Income Taxes    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 0 0
Regulatory liabilities, long -term 128,886 131,480
Plant Removal Obligations    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 8,456 8,509
Regulatory liabilities, long -term 117,359 105,733
Fuel Clause Adjustments    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 12,217 365
Regulatory liabilities, long -term $ 0 0
Regulatory liabilities - Remaining Recovery/Refund Period 1 year  
Alternative Revenue Program Riders    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current $ 8,426 2,504
Regulatory liabilities, long -term $ 0 0
Regulatory liabilities - Remaining Recovery/Refund Period 1 year  
North Dakota PTC Refunds    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current $ 0 0
Regulatory liabilities, long -term 10,281 7,136
Pension and Other Postretirement Benefit Plans    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 2,279 5,589
Regulatory liabilities, long -term 19,026 0
Other    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 907 333
Regulatory liabilities, long -term 257 148
Pension and Other Postretirement Benefit Plans    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 0 0
Regulatory assets, long-term 86,286 88,354
Alternative Revenue Program Riders    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 5,780 5,679
Regulatory assets, long-term $ 118 2,508
Regulatory assets - Remaining Recovery/Refund Period 2 years  
Asset Retirement Obligations    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 0 0
Regulatory assets, long-term 0 1,467
Deferred Income Taxes    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 0 0
Regulatory assets, long-term 931 0
ISO Cost Recovery Trackers    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 144 575
Regulatory assets, long-term $ 260 314
Regulatory assets - Remaining Recovery/Refund Period 2 years  
Unrecovered Project Costs    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 349 320
Regulatory assets, long-term $ 962 990
Regulatory assets - Remaining Recovery/Refund Period 4 years  
Deferred Rate Case Expenses    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 377 377
Regulatory assets, long-term $ 471 754
Regulatory assets - Remaining Recovery/Refund Period 3 years  
Fuel Clause Adjustments    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 9,141 10,893
Regulatory assets, long-term $ 0 0
Regulatory assets - Remaining Recovery/Refund Period 1 year  
Derivative Instruments    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 1,225 7,130
Regulatory assets, long-term $ 228 0
Regulatory assets - Remaining Recovery/Refund Period 2 years  
Other    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 25 25
Regulatory assets, long-term $ 235 $ 268